1. Field of the Invention
The present invention relates to by-product coke ovens and, more particularly, to methods for sealing such coke ovens against the leakage of smoke, dust and noxious by-product gases.
2. Description of the Prior Art
Under current technology, the manufacture of metals and their alloys generally involves refining a quantity of industrially pure metal from its ore. In the case of iron and steelmaking, industrially pure iron is produced by the reduction of iron oxide in a blast furnace. Due to the large quantity of iron which is annually refined, a large quantity of a relatively inexpensive reducing agent is required for the blast furnace reduction process.
The best reducing agent available in the quantities demanded by the blast furnace reduction process has been found to be coke. Coke is obtained by the destruction distillation of selected coals at temperatures typically in the range of 1,650.degree. F. to 2,000.degree. F. Generally, this destruction distillation process is carried on in a retort known as a by-product coke oven. The coke oven is a chamber that is typically eight to twenty feet high, thirty-five to fifty feet long, and twelve to eighteen inches wide. The ovens are laterally arranged in groups, called batteries, to improve their heating efficiency. Various doors are associated with each oven, which include pushing doors, coking doors, chuck doors, charging lids, and elbow covers. Various fluids are carried to and from the oven by pipes and conduits that are connected to the oven by slip-joints.
In the operation of the coke oven, the pushing and coking doors are engagingly set into their respective doorways on opposite ends of the oven, and the oven is filled with coking coal through charging holes in the top of the oven. Charging lids are then placed over the charging holes and the coal in the oven is leveled by a leveling bar inserted through a chuck door opening in the pushing door. When the coal is level, the leveling bar is removed and the chuck door is closed. The oven is then heated until the distillation process is completed after a period of typically 16 to 28 hours. During this period, by-product fluids of the coking process such as flue gas, ammonium sulphate, phenal, naphthalene, benzene, and other fluids are removed as off-gases through an ascension pipe at the top of the coke oven. At the end of the distillation process the pushing and coking doors are removed. A ram is then inserted through the pushing doorway and caused to travel the length of the oven such that the coke is pushed through the coking doorway of the oven into a larry car. The ram is then withdrawn, and the pushing and coking doors replaced in their respective doorways to prepare the oven for the next coking operation cycle.
In addition to the above mentioned doorways, the coke oven is in communication with various other pipes and conduits. For example, each battery of coke ovens is provided with a gas collecting system in which volatile products that are liberated in the coke oven during the coking process are removed from the oven and provided to the gas recovery units. Typically, these gas collecting systems include an ascension pipe or standpipe associated with each coke oven and a collecting main that is connected to all the standpipe of the battery. The volatile gases of each coke oven are carried through respective standpipes to the collecting main which transports the collected gas to the recovery units and the gas products to the tar decanters. Each standpipe is connected to the coke oven by a sealed slip-joint that accomodates the thermal expansion and contraction of the standpipes. Many other examples of the use of such slip-joints also exist.
A pronounced problem in coke oven technology has been the sealing of the coke oven to prevent emissions of gas, dust and smoke during the coking cycle. In the prior art, several techniques for sealing various common emission points of coke ovens have been developed. From the early history of the coking industry, one method for sealing coke oven doors has been to manually place a packing material at the interface between the doorway and the door. This method, known as luting, proved to be unsatisfactory in several respects. First, luting was found to be of limited efficiency for the reason that, over the coking cycle, the luting material would dry and develop cracks through which emissions could pass. Also, with the increased mechanization of coke production, luting came to be recognized as being labor intensive and a hindrance to rapid production, and, consequently, expensive. In addition, the luting process required residual luting material to be cleaned from the door and door jamb at the termination of each coking cycle so that a new application of luting material could be made for the next coking cycle. This residual luting material was difficult to remove. The additional step of cleaning away the residual luting material increased the labor demands of the luting process and further limited significantly the rate at which coke could be produced. Indeed, the luting process as applied to coke oven doors, proved to be slow for use in modern coke ovens in which the entire coking operation is highly mechanized. Today luting of coke oven doors is used only in a few coke oven batteries of small size.
Today coke ovens generally use self-sealing doors. In these doors, a sealing edge is comprised of a knife-edge or a spring loaded stainless-steel strip mounted on a flexible diaphram that adjusts to the contour of the door jamb sealing face. U.S. Pat. Nos. 3,032,483, 2,965,550, 2,207,652, 3,172,825, 3,510,404, and 2,855,347 describe exemplary coke oven doors of this type known to the applicants. The problem with these coke oven doors is that, in view of the size of coke oven doors, even with a diaghram mechanism it is extremely difficult to attain a tight fit over the entire contour of the seal. Furthermore, the doors, which must be set and removed during each coking cycle, are cumbersome to manipulate due to their size and weight so that the seals for this type of door, which are delicate in comparison to the door itself, are frequently damaged during the operation of the coke oven. Also, thermal stresses set up by the coke oven heat cause warping to the degree that a tight seal around the door cannot be maintained. Furthermore, in all cases and particularly where a seal does not form a tight fit, in the operation of the coke oven, tar deposits accumulate on the face of the door jamb which make the face increasingly irregular and a tight seal with the door increasingly more unlikely. Although cleaning machinery for removing these tar deposits has been developed and regular cleaning schedules are commonly established, the tar deposits are extremely difficult to remove and such cleaning operations are not adequately effective. Furthermore, the coke oven attendants are exposed to adverse thermal and ambient working conditions during a typical cleaning process. Therefore, the attendants are understandably reluctant to perform this task and, pragmatically, the schedule for cleaning the doors and door jambs is often not maintained. In any event, such cleaning operations are time consuming and do nothing to remedy the failure to form a tight seal caused by thermal stresses and structural deformations. Indeed, the cleaning operations themselves are one source of such deformations.
Yet another method for sealing coke oven doors has been the injection of coke oven gas through the doors, and from there into the open area around the door seals such as described in German Pat. No. 1,149,330. The injected gas provides a higher pressure at the door seal area to prevent escape of tarry smoke and vapors from the oven interior to the outside. This method has also been adapted to inject the coke oven gas into the door seal area through the door jambs instead of the doors themselves. The problem with this method of sealing oven doors has been that a significant portion of the coke oven gas escapes from the seal area into the atmosphere where it cannot be recovered to provide supplemental heating of the coke oven. Also, the coke oven gas deposited a residue of fluff carbon around the seal area. Although this fluff carbon was found to break up under normal mechanical cleaning methods more easily than tar deposited directly on the door or door jamb, thereby acting as a barrier to the deposition of tar on the door or door jamb, periodic cleaning of the door jamb face and the inner face of the doors was nevertheless required.
Another method of sealing coke oven doors included the use of a heat settable sealant as described in U.S. Pat. No. 3,875,018. As therein proposed, a coke oven door is provided with a passage for the injection of a heat settable sealant which acts as a seal between the door and the door jamb. Initially, the injected heat settable sealant is in fluid form, but after exposure to heat at the perimeter of the door, the sealant solidifies. The solid sealant hardens with a glazed-like surface that facilitates removal of the solid sealant at the completion of the coking cycle. This method, however, suffered from several disadvantages. First, the requirement of new doors having a passage for injection of the heat settable sealant or the equivalent modification of existing doors demanded a large initial capital investment from the user. Also, unless a liquid-tight seal initially existed, crevices between the door and door jamb in combination with the initial liquid state of the sealant created the potential for waste of large amounts of sealant, at least until the sealant had solidified sufficiently to stop flowing and block the flow of liquid sealant at the crevice. Also, the tendency of the sealant to harden permitted emittant leakage around the sealant as a consequence of coke even expansion and contraction under thermal stresses.
In the prior art, the problem of adequately sealing the doors each time they are set in the doorway has presisted. U.S. Pat. Nos. 2,571,597; 1,790,775; 725,746; 1,056,270; 2,878,170; 1,918,760 and 2,662,053 are considered to be further illustrative of the prior art. With regard to the sealing of slip-joints and similar points for potential emission of gas, dust, and smoke, a procedure somewhat similar to the method of sealing doors by luting is still the primary procedure. When the luting material cracks or otherwise deteriorates to a condition such that emittants begin to leak from the slip joints, the luting material must be removed. Removal of luting material at such slip-joints, which is done manually is very difficult and time consuming. Typically slip joint seals of luting material are removed by mechanically chipping or water blast processes. Luting materials used on slip joints include various refractory materials and an asbestos treated rope. Typically, lifetimes of such materials are in the range of one day to six months although longer and shorter periods of service are obtained.
While the luting materials themselves are relatively inexpensive, considerable labor is required to remove the hardened luting material of the old seal and apply to new material. In a typical example, replacement of fifteen standpipe seals for a coke oven battery requires the labor of a three-man crew for two shifts. This equates to three hours and twelve minutes labor for each seal that is changed. It is apparent, therefor, that there was a need for a more convenient, quicker, and inexpensive method for sealing slip-joints such as those connecting the coke oven with pipes and conduits for carrying off-gases of by-product coke ovens.
The imperfect sealing of the coke ovens permitted dust, smoke and noxious by-products of the coking process to escape from the oven. This condition is aggrevated by the fact that a positive pressure is maintained in the oven to prevent the admittance of air into the coking chamber which would seriously damage the quality of coke produced. In the past, the escape of a certain portion of smoke and coking by-products was tolerated to the extent that it did not effect the quality of the coke produced and was the only commercially practicable manner for producing coke. More recently, however, the growing awareness of the environmental implications which the release of such smoke and noxious by-products present, together with a growing concern for the health of persons exposed to such emmittants has made the prior art sealing methods increasingly unacceptable.
The disclosed invention overcomes the problems and difficulties of te prior art by providing a method for sealing coke ovens which is effective to prevent the escape of dust, smoke, coke oven gas, and other coking by-products from the oven during the coking cycle to improve the general environmental impact of the coke oven as well as to conserve the quantity of fuel consumed and the by-products which are produced. In providing these improvements, the disclosed method requires minimal attention and care from coke oven attendants, thus assuring its effectiveness over many coking operation cycles of the oven. Additionally, the method requires no capital investment in new coke oven structures or modifications to existing structures thereby assuring its economic practicality.